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Peter J Meier

Publications and source records attributed to Peter J Meier.

At least 37 records · Page 2Linked to original sources
PubMed2004

Vectorial transport of bile salts across MDCK cells expressing both rat Na+-taurocholate cotransporting polypeptide and rat bile salt export pump.

Bile salts are predominantly taken up by hepatocytes via the basolateral Na(+)-taurocholate cotransporting polypeptide (NTCP/SLC10A1) and secreted into the bile by the bile salt export pump (BSEP/ABCB11). In the present study, we transfected rat Ntcp and rat Bsep into polarized Madin-Darby canine kidney cells and characterized the transport properties of these cells for eight bile salts. Immunohistochemical staining demonstrated that Ntcp was expressed at the basolateral domains, whereas Bsep was expressed at the apical domains. Basal-to-apical transport of taurocholate across the monolayer expressing only Ntcp and that coexpressing Ntcp/Bsep was observed, whereas the flux across the monolayer of control and Bsep-expressing cells was symmetrical. Basal-to-apical transport of taurocholate across Ntcp/Bsep-coexpressing monolayers was significantly higher than that across monolayers expressing only Ntcp. Kinetic analysis of this vectorial transport of taurocholate gave an apparent K(m) value of 13.9 +/- 4.7 microM for cells expressing Ntcp alone, which is comparable with 22.2 +/- 4.5 microM for cells expressing both Ntcp and Bsep and V(max) values of 15.8 +/- 4.2 and 60.8 +/- 9.0 pmol.min(-1).mg protein(-1) for Ntcp alone and Ntcp and Bsep-coexpressing cells, respectively. Transcellular transport of cholate, glycocholate, taurochenodeoxycholate, chenodeoxycholate, glycochenodeoxycholate, tauroursodeoxycholate, ursodeoxycholate, and glycoursodeoxycholate, but not that of lithocholate was also observed across the double transfectant. This double-expressing system can be used as a model to clarify vectorial transport of bile salts across hepatocytes under physiological conditions.

Adenoviridae↗
PubMed2004

Small hepatocytes in culture develop polarized transporter expression and differentiation.

Rat small hepatocytes have been shown to proliferate in culture and to form organoids with differentiated hepatocytes in vitro. To evaluate the degree of polarized transporter differentiation of rat small hepatocytes during 9 weeks of culturing, we studied the time-dependent expression and subcellular localization of the major bile salt and organic anion transport systems of hepatocytes [i.e. the basolateral sodium-taurocholate co-transporting protein (Ntcp), organic-anion-transporting polypeptide 1b2 (Oatp1b2), the canalicular bile-salt export pump (Bsep) and multidrug-resistance-associated protein 2 (Mrp2)]. Small hepatocytes proliferated and differentiated in culture and formed sharply demarcated colonies as assessed by morphology, alpha-fetoprotein, albumin and Mrp1 expression. Polarized surface transporter expression was evident after 5 weeks of culturing for Ntcp, Oatp1b2 and Mrp2, and after 7 weeks for Bsep. After 9 weeks in culture, the vast majority of matured hepatocytes expressed Ntcp/Oatp1b2 at the basolateral and Bsep/Mrp2 at the canalicular plasma-membrane domains. This polarized transporter expression was accompanied by canalicular secretion of fluorescein-diacetate and cholylglycyl-fluorescein. Furthermore, an anastomizing three-dimensional network of bile canaliculi developed within piling-up colonies. These data demonstrate that cultured rat small hepatocytes acquire a fully differentiated transporter expression phenotype during their development into hepatic 'organoid-like' clusters of mature hepatocytes. Thereby, the time-dependent sequence of transporter expression mirrored the ontogenesis of transporter expression in developing rat liver, supporting the concept that small hepatocytes correspond to the hepatocyte lineage derived from embryonic hepatoblasts and/or from a different pool of 'committed hepatocyte progenitor cells'.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2004

BSEP and MDR3 haplotype structure in healthy Caucasians, primary biliary cirrhosis and primary sclerosing cholangitis.

Primary biliary cirrhosis (PBC) and primary sclerosing cholangitis (PSC) are characterized by a cholestatic pattern of liver damage, also observed in hereditary or acquired dysfunction of the canalicular membrane transporters bile salt export pump (BSEP, ABCB11) and multidrug resistance protein type 3 (MDR3, ABCB4). Controversy exists whether a genetically determined dysfunction of BSEP and MDR3 plays a pathogenic role in PBC and PSC. Therefore, 149 healthy Caucasian control individuals (control group) were compared to 76 PBC and 46 PSC patients with respect to genetic variations in BSEP and MDR3. Sequencing spanned approximately 10,000 bp including promoter and coding regions as well as 50-350 bp of flanking intronic regions. In all, 46 and 45 variants were identified in BSEP and MDR3, respectively. No differences between the groups were detected either in the total number of variants (BSEP: control group: 37, PBC: 37, PSC: 31; and MDR3: control group: 35; PBC: 32, PSC: 30), or in the allele frequency of the common variable sites. Furthermore, there were no significant differences in haplotype distribution and linkage disequilibrium. In conclusion, this study provides an analysis of BSEP and MDR3 variant segregation and haplotype structure in a Caucasian population. Although an impact of rare variants on BSEP and MDR3 function cannot be ruled out, our data do not support a strong role of BSEP and MDR3 genetic variations in the pathogenesis of PBC and PSC.

ATP Binding Cassette Transporter, Subfamily B↗
PubMed2004

The human organic anion transporting polypeptide 8 (SLCO1B3) gene is transcriptionally repressed by hepatocyte nuclear factor 3beta in hepatocellular carcinoma.

BACKGROUND/AIMS: The organic anion transporting polypeptides (OATPs) mediate the uptake of numerous amphipathic compounds into hepatocytes. Our aim was to study the expression and regulation of OATP8 (OATP1B3, SLC21A8/SLCO1B3) and OATP-C (OATP1B1, SLC21A6/SLCO1B1) in hepatocellular carcinomas (HCC). METHODS: RNA and protein levels in 13 paired HCC and adjacent non-tumor liver samples were quantified by real-time polymerase chain reaction or Western blot, respectively. The OATP8 and OATP-C gene promoters were characterized by luciferase reporter assays and electrophoretic mobility shift assays (EMSA). RESULTS: The expression of OATP8 was decreased in 60% of HCC compared to surrounding non-tumor liver tissue, on both the mRNA and protein levels. Expression of the liver-enriched transcription factor hepatocyte nuclear factor 3beta (HNF3beta) was increased in 70% of HCC and correlated inversely with OATP8 mRNA (r=-0.75, P<0.05) and protein. In contrast to OATP8, expression of OATP-C was not significantly decreased in HCC. In transfected Huh7 cells, OATP8 promoter activity was inhibited by 70% when HNF3beta was cotransfected. An HNF3beta binding site was located at nt -39/-23 by EMSA. The OATP-C promoter was not inhibited by HNF3beta. CONCLUSIONS: HNF3beta represses transcription of the OATP8 but not the OATP-C gene, providing a mechanism for reduced expression of OATP8 in HCC.

Aged↗
PubMed2004

Differential expression of bile salt and organic anion transporters in developing rat liver.

BACKGROUND/AIMS: Differentiated hepatocytes express distinct transport systems at their basolateral and canalicular membrane domains. Here, we investigated the ontogenesis of the polar expression of hepatocellular organic anion and bile salt transport systems in rat liver. METHODS: mRNA levels (real time PCR) and protein expression (immunofluorescence microscopy) were investigated for the Na(+)-taurocholate cotransport protein (Ntcp), the organic anion transporting polypeptides (Oatp1a1, Oatp1a4, Oatp1b2), the multidrug resistance associated proteins (Mrp2, Mrp6) and the bile salt export pump (Bsep). RESULTS: Expression of mRNA and protein was detected first for Oatp1b2, Mrp2 and Mrp6 at embryonic day 16 (E16), followed by Ntcp, Oatp1a1 and Bsep at E20 and by Oatp1a4 at postnatal day 5 (P5). Intracellular localization of Oatps (e.g. Oatp1b2) preceded expression at the plasma membrane. Approximate adult phenotypes of polarized expression were achieved for Ntcp by P5, for Bsep, Mrp2 and Mrp6 by P12 and for Oatp1a1, Oatp1a4 and Oatp1b2 by P29. CONCLUSIONS: The data demonstrate that full maturation of polarized transporter expression in rat liver requires several weeks. The findings provide a molecular explanation for the previously observed chronology of the functional maturation of bile salt-independent and dependent bile formation and of hepatic detoxification functions in developing rat liver.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2004

P-glycoprotein expression, localization, and function in sandwich-cultured primary rat and human hepatocytes: relevance to the hepatobiliary disposition of a model opioid peptide.

PURPOSE: The isolation of hepatocytes from intact liver involves collagenase digestion of the tissue, resulting in loss of cell polarization and functional vectorial excretion. These studies examined repolarization, localization of P-glycoprotein (P-gp) to the canalicular domain of the hepatocyte, and re-establishment of vectorial transport in sandwich-cultured (SC) rat and human primary hepatocytes. METHODS: Protein localization and expression were determined in SC hepatocytes by confocal microscopy and Western blotting, respectively. Transporter function was evaluated by measuring [D-penicillamine2,5]enkephalin (3H-DPDPE) and 5 (and 6)-carboxy-2',7'-dichlorofluorescein (CDF) biliary excretion in SC hepatocytes. RESULTS: P-gp and the canalicular marker protein dipeptidyl peptidase IV (DPPIV) co-localized by Day 3 and Day 6 in SC rat hepatocytes and SC human hepatocytes, respectively, consistent with canalicular network formation visualized by light microscopy. Co-localization of multidrug resistance associated protein 2 (MRP2) and P-gp in SC human hepatocytes was observed on Day 6 in culture. Expression levels of P-gp increased slightly in both species over days in culture; similar expression was observed for MRP2 in SC human hepatocytes. Oatp1a1 expression in SC rat hepatocytes was maintained over days in culture, whereas Oatp1a4 expression decreased. OATP1B1 expression decreased slightly on Day 3 in SC human hepatocytes. OATP1B3 expression was constant in SC human hepatocytes. In vitro biliary excretion of the opioid peptide 3H-DPDPE correlated with the proper localization of canalicular proteins in both species. Excretion of CDF in SC human hepatocytes confirmed network formation and MRP2 function. CONCLUSIONS: These studies indicate that SC hepatocytes repolarize and traffic functional canalicular transport proteins to the appropriate cellular domain.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2004

Enterohepatic bile salt transporters in normal physiology and liver disease.

The vectorial transport of bile salts from blood into bile is essential for the generation of bile flow, solubilization of cholesterol in bile, and emulsification of lipids in the intestine. Major transport proteins involved in the enterohepatic circulation of bile salts include the hepatocellular bile salt export pump (BSEP, ABCB11), the apical sodium-dependent bile salt transporter (ASBT, SLC10A2) in cholangiocytes and enterocytes, the sodium-dependent hepatocyte bile salt uptake system NTCP (SLC10A1), the organic anion transporting polypeptides OATP-C (SLC21A6), OATP8 (SLC21A8) and OATP-A (SLC21A3), and the multidrug resistance protein MRP3 (ABCC3). Synthesis and transport of bile salts are intricately linked processes that undergo extensive feedback and feed-forward regulation by transcriptional and posttranscriptional mechanisms. A key regulator of hepatocellular bile salt homeostasis is the bile acid receptor/farnesoid X receptor FXR, which activates transcription of the BSEP and OATP8 genes and of the small heterodimer partner 1 (SHP). SHP is a transcriptional repressor that mediates bile acid-induced repression of the bile salt uptake systems rat Ntcp and human OATP-C. A nuclear receptor that activates rodent Oatp2 (Slc21a5) and human MRP2 (ABCC2) is the pregnane X receptor/steroid X receptor PXR/SXR. Intracellular trafficking and membrane insertion of bile salt transporters is regulated by lipid, protein, and extracellular signal-related kinases in response to physiologic stimuli such as cyclic adenosine monophosphate or taurocholate. Finally, dysfunction of individual bile salt transporters such as BSEP, on account of genetic mutations, steric inhibition, suppression of gene expression, or disturbed signaling, is an important cause of cholestatic liver disease.

Animals↗
PubMed2004

The clinical picture of olanzapine poisoning with special reference to fluctuating mental status.

BACKGROUND: Olanzapine is an atypical antipsychotic drug that is increasingly used in intentional drug overdoses. Although acute olanzapine overdose is predominantly associated with anticholinergic symptoms and central nervous system depression, miosis and unpredictable fluctuations between somnolence/coma and agitation/ aggression have been suggested as typical signs of olanzapine intoxication in single case reports. AIMS: To confirm the suggestion that fluctuating central nervous system changes and miosis are characteristic signs of olanzapine intoxication. To estimate the dose-response relationship as a guide for the provision of optimal management of olanzapine intoxicated patients. METHODS: Retrospective analysis of all well-documented cases of olanzapine intoxication reported to the Swiss Toxicological Information Centre between January 1997 and October 2001. Inclusion criteria for detailed analysis were patient age > or = 16 yr, acute olanzapine monointoxication, ingested dose > 20 mg, and a causal relationship between olanzapine overdose and clinical effects. The Poisoning Severity Score of the European Association of Poison Centres and Clinical Toxicologists (EAPCCT) assessed the intoxication severity. RESULTS: Out of a total of 131 cases of olanzapine overdose, 26 cases fulfilled the inclusion criteria. The ingested olanzapine doses ranged from 30 to 840 mg. The most frequent findings were somnolence (77%), agitation (42%), and miosis (31%). The Poisoning Severity Score was "minor" in 14 (54%), "moderate" in 11 (42%), and "severe" in 1 (4%) patients. Nine patients (35% of all patients) with moderate olanzapine poisoning (120-840 mg) showed unpredictable fluctuations between somnolence and agitation. Five of these patients also demonstrated marked miosis. All patients recovered within 48h. One patient with severe poisoning (560 mg) had coma and convulsions. Moderate (and severe) symptoms occurred only at ingested doses above 120 mg. There was a statistically significant association between increasing ingested olanzapine doses and poisoning severity. CONCLUSIONS: Although olanzapine is tolerated relatively well in acute overdose, unpredictable and transient fluctuations between central nervous system depression and agitation, frequently associated with miosis, appear to be characteristic findings in moderate to high olanzapine overdoses. They are transient in nature and require careful clinical monitoring but rarely require specific therapeutic interventions.

Activity Cycles↗
PubMed2004

Metal-responsive transcription factor-1 (MTF-1) is essential for embryonic liver development and heavy metal detoxification in the adult liver.

Metal-responsive transcription factor-1 (MTF-1) activates the transcription of metallothionein genes and other target genes in response to heavy metal load and other stresses such as hypoxia and oxidative stress. It also has an essential function during embryogenesis: targeted disruption of Mtf1 in the mouse results in lethal liver degeneration on day 14 of gestation. Here we studied Mtf1 knockout mice at embryonic and adult stages, the latter by means of conditional knockout. Hepatocytes from Mtf1 null mutant and wild-type embryos were taken into culture on day 12.5 of gestation. Both initially appeared normal, but mutant cells were lost within a few days. Furthermore, Mtf1 null hepatocytes were poorly, if at all, rescued by cocultivation with wild-type rat embryo hepatocytes, indicating a cell-autonomous defect. When the Mtf1 gene was excised by Cre recombinase after birth in liver and bone marrow and to a lesser extent in other organs, mice were viable under non-stress conditions but highly susceptible to cadmium toxicity, in support of a role of MTF-1 in coping with heavy metal stress. An additional MTF-1 function was revealed upon analysis of the hematopoietic system in conditional knockout mice where leukocytes, especially lymphocytes, were found to be severely underrepresented. Together, these findings point to a critical role of MTF-1 in embryonic liver formation, heavy metal toxicity, and hematopoiesis.

Animals↗
PubMed2004

Sequence analysis of bile salt export pump (ABCB11) and multidrug resistance p-glycoprotein 3 (ABCB4, MDR3) in patients with intrahepatic cholestasis of pregnancy.

Intrahepatic cholestasis of pregnancy (ICP) is a liver disorder associated with increased risk of intrauterine fetal death and prematurity. There is increasing evidence that genetically determined dysfunction in the canalicular ABC transporters bile salt export pump (BSEP, ABCB11) and multidrug resistance protein 3 (MDR3, ABCB4) might be risk factors for ICP development. This study aimed to (i). describe the extent of genetic variability in BSEP and MDR3 in ICP and (ii). identify new disease-causing mutations. Twenty-one women with ICP and 40 women with uneventful pregnancies were recruited between April 2001 and April 2003. Sequencing of BSEP and MDR3 spanned 8-10 kb per gene and comprised the promoter region and 100-350 bp of the flanking intronic region around each exon. DNA sequencing of polymerase chain reaction fragments was performed on an ABI3700 capillary sequencer. MDR3 promoter activity of promoter constructs carrying different ICP-specific mutations was studied using reporter assays. A total of 37 and 51 variant sites were detected in BSEP and MDR3, respectively. Three non-synonymous sites in codons for evolutionarily conserved amino acids were specific for the ICP collective (BSEP, N591S; MDR3, S320F and G762E). Furthermore, four ICP-specific splicing mutations were detected in MDR3 [intron 21, G(+1)A; intron 25, G(+5)C and C(-3)G; and intron 26, T(+2)A]. Activity of the mutated MDR3 promoter was similar to that observed for the wild-type promoter. Our data further support an involvement of MDR3 genetic variation in the pathogenesis of ICP, whereas analysis of BSEP sequence variation indicates that this gene is probably less important for the development of pregnancy-associated cholestasis.

ATP Binding Cassette Transporter, Subfamily B↗
PubMed2004

Gd-BOPTA transport into rat hepatocytes: pharmacokinetic analysis of dynamic magnetic resonance images using a hollow-fiber bioreactor.

RATIONALE AND OBJECTIVES: To investigate the transport of the hepatobiliary magnetic resonance (MR) imaging contrast agent Gd-BOPTA into rat hepatocytes. MATERIALS AND METHODS: In a MR-compatible hollow-fiber bioreactor containing hepatocytes, MR signal intensity was measured over time during the perfusion of Gd-BOPTA. For comparison, the perfusion of an extracellular contrast agent (Gd-DTPA) was also studied. A compartmental pharmacokinetic model was developed to describe dynamic signal intensity-time curves. RESULTS: The dynamic signal intensity-time curves of the hepatocyte hollow-fiber bioreactor during Gd-BOPTA perfusion were adequately fitted by 2 compartmental models. Modeling permitted to discriminate between the behaviors of the extracellular contrast agent (Gd-DTPA) and the hepatobiliary contrast agent (Gd-BOPTA). It allowed the successfully quantification of the parameters involved in such differences. Gd-BOPTA uptake was saturable at high substrate concentrations. CONCLUSIONS: The transport of Gd-BOPTA into rat hepatocytes was successfully described by compartmental analysis of the signal intensity recorded over time and supported the hypothesis of a transporter-mediated uptake.

Animals↗
PubMed2004

Effect of dexamethasone treatment on the expression and function of transport proteins in sandwich-cultured rat hepatocytes.

Dexamethasone (DEX) is a well established inducer of CYP3A. These studies examined the influence of DEX treatment on transport protein expression and function in sandwich-cultured (SC) rat hepatocytes. Freshly isolated hepatocytes were cultured between two layers of gelled collagen and maintained in Dulbecco's modified Eagle's medium supplemented with DEX (0.1 microM, 0-48 h and 0.1-100 microM, 48-96 h). The expression of sinusoidal [(organic anion transporting polypeptide 1a1 (Oatp1a1), Oatp1a4, multidrug resistance-associated protein 3 (Mrp3), and Na(+)-dependent taurocholate cotransporting polypeptide (Ntcp)] and canalicular [bile salt export pump (Bsep), multidrug resistance protein 1a/b (Mdr1a/b), and Mrp2] transport proteins was determined by Western blot analysis. The accumulation and biliary excretion index (BEI; percentage of accumulated substrate in canalicular networks) of the probe substrates taurocholate (TC; 1 microM, 10 min), rhodamine 123 (Rh123; 10 microM, 30 min), and carboxy-2',7'-dichlorofluorescein (CDF; 10 microM, 10 min) were employed as measures of canalicular transport protein function in SC rat hepatocytes. DEX treatment increased CYP3A1/2, Oatp1a4, and Mrp2 expression, decreased the expression of Ntcp, and did not seem to alter the expression of Oatp1a1, Mrp3, Mdr1a/b, or Bsep. The BEI of CDF, an Mrp2 substrate, increased from 18 to 37% after DEX treatment (100 microM). The accumulation of TC, an Ntcp substrate, was reduced (<50% of control), whereas the BEI of TC, also a Bsep substrate, was unchanged. Treatment of SC rat hepatocytes with DEX resulted in alterations in the expression of CYP3A1/2 and some hepatic transport proteins. Modest alterations in hepatic transport protein function were consistent with changes in protein expression.

Animals↗
PubMed2004

Agonist-induced internalization of leukotriene B(4) receptor 1 requires G-protein-coupled receptor kinase 2 but not arrestins.

The leukotriene B(4) (LTB(4)) receptor (BLT1) becomes desensitized upon repeated agonist stimulation. Little is known, however, about BLT1 internalization, which follows desensitization in most G-protein-coupled receptors (GPCR). In the current study, transiently expressed BLT1 readily internalized, after LTB(4) stimulation, in RBL-2H3 cells that express high levels of endogenous GPCR kinase 2 (GRK2) but did not in COS-7 or human embryonic kidney (HEK) 293 cells, which do not overexpress GRK. The internalization of BLT1 could be blocked in RBL-2H3 cells by coexpressing dominant-negative (DN) GRK2 K220R and could be promoted in HEK293 cells by coexpressing wild-type (WT) GRK2. Coexpression of WT or DN nonvisual arrestins had no effect on BLT1 internalization. Moreover, upon stimulation with LTB(4), BLT1 did not induce arrestin-green fluorescence protein redistribution in either cell type, even in the presence of overexpressed GRK2. Coimmunoprecipitation experiments confirmed that BLT1 could associate with GRK2 but not with arrestins. A C-tail-truncated mutant of BLT1 lost the capacity to internalize and associate with GRK2 upon exposure to LTB(4), suggesting that the C-tail was required for receptor internalization and association with GRK2. Taken together, our results indicate that the C terminus of BLT1 plays a pivotal role in receptor internalization and GRK2 association. Moreover, ligand-induced BLT1 internalization is dependent on GRK2 but independent of arrestins. This may allow differential, cell-type-specific signaling in response to LTB(4), depending on GRK expression levels.

Animals↗
PubMed2003

Role of liver-enriched transcription factors and nuclear receptors in regulating the human, mouse, and rat NTCP gene.

Hepatic uptake of bile acids is mediated by the Na(+)-taurocholate cotransporting polypeptide (NTCP; SLC10A1) of the basolateral hepatocyte membrane. Several cis-acting elements in the rat Ntcp gene promoter have been characterized. However, little is known about the mechanisms that control the expression of the human or mouse NTCP/Ntcp. We, therefore, compared the transcriptional regulation of the human and mouse NTCP/Ntcp gene with that of the rat. By computer alignment, a sequence in the 5'-regulatory region that is conserved between species was identified near the transcription start site. Huh7 cells were transfected with luciferase constructs containing the conserved region from each species. The hepatocyte nuclear factors (HNF)1alpha and -4alpha and the retinoid X receptor/retinoic acid receptor dimer (RXRalpha/RARalpha) bound and transactivated the rat but not the human or mouse NTCP/Ntcp promoters. In contrast, activation by the CCAAT/enhancer binding protein-beta was specific for human and mouse NTCP/Ntcp. The only consensus motif present in all three species was HNF3beta. HNF3beta formed a specific DNA-protein complex in electrophoretic mobility shift assays and inhibited NTCP/Ntcp promoter activity in cotransfection assays. Finally, a minor repressive effect of bile acids was only found for rat Ntcp. The transcriptional repressor small heterodimer partner (SHP) did not affect NTCP/Ntcp promoter activity. We conclude that 1) the transcriptional regulation of the conserved NTCP/Ntcp 5'-regulatory region differs considerably among human, mouse, and rat; and 2) the conserved NTCP/Ntcp regulatory region is not directly regulated by SHP. Bile acids may regulate NTCP/Ntcp indirectly by modulating the capacity of nuclear factors to activate gene expression.

Animals↗
PubMed2003

Organic anion transporting polypeptides of the OATP/ SLC21 family: phylogenetic classification as OATP/ SLCO superfamily, new nomenclature and molecular/functional properties.

The organic anion transporting polypeptides (rodents: Oatps, human: OATPs) form a superfamily of sodium-independent transport systems that mediate the transmembrane transport of a wide range of amphipathic endogenous and exogenous organic compounds. Since the traditional SLC21 gene classification does not permit an unequivocal and species-independent identification of genes and gene products, all Oatps/OATPs are newly classified within the OATP/ SLCO superfamily and subdivided into families (>/=40% amino acid sequence identity), subfamilies (>/=60% amino acid sequence identity) and individual genes and gene products according to their phylogenetic relationships and chronology of identification. Implementation of this new classification and nomenclature system occurs in agreement with the HUGO Gene Nomenclature Committee (HGNC). Among 52 members of the OATP/ SLCO superfamily, 36 members have been identified so far in humans, rat and mouse. The latter are clustered within 6 (out of 12) families (OATP1-OATP6) and 13 subfamilies. Oatps/OATPs represent 12 transmembrane domain proteins and contain the superfamily signature D-X-RW-(I,V)-GAWW-X-G-(F,L)-L. Although species divergence, multispecificity and wide tissue distribution are common characteristics of many Oatps/OATPs, some members of the OATP/ SLCO superfamily are highly conserved during evolution, have a high substrate specificity and exhibit unique cellular expression in distinct organs. Hence, while Oatps/OATPs with broad substrate specificity appear to play an important role in the bioavailability, distribution and excretion of numerous exogenous amphipathic organic anionic compounds, Oatps/OATPs with a narrow spectrum of transport substrates may exhibit more specific physiological functions in distinct organs.

Animals↗
PubMed2003

Regulation of basolateral organic anion transporters in ethinylestradiol-induced cholestasis in the rat.

BACKGROUND/AIMS: Estrogen-mediated cholestasis is an important clinical entity, but its molecular pathophysiology is still not fully understood. Impaired sodium-dependent uptake of bile acids has been associated with diminished expression of a basolateral Na(+)/bile acid cotransporter (Ntcp), whereas sodium-independent uptake is maintained despite a down-regulation of the organic anion transporter Oatp1. Thus, expression of the two other rat Oatps (Oatps2 and -4) was determined in estrogen-induced cholestasis. In addition, known transactivators of Oatp2 and Ntcp were studied to further characterize transcriptional regulation of these transporter genes. METHODS: Hepatic protein and mRNA expression of various Oatps (1, 2, 4) in comparison to Ntcp were analyzed after 0.5, 1, 3 and 5 days of ethinylestradiol (EE) treatment (5 mg/kg) in rats. Binding activities of Oatp2 and Ntcp transactivators were assessed by electrophoretic mobility shift assays. RESULTS: All basolateral Oatps (1, 2 and 4) were specifically down-regulated at the protein level by 30-40% of controls, but less pronounced than Ntcp (minus 70-80%). In contrast to unaltered Oatp4 mRNA levels, Oatp1 and Oatp2 mRNAs were reduced to various extents (minus 40-90% of controls). Binding activity of known transactivators of Ntcp and Oatp2 such as hepatocyte nuclear factor 1 (HNF1), CAAT enhancer binding protein alpha (C/EBPalpha) and pregnane X receptor (PXR) were also diminished during the time of cholestasis. CONCLUSIONS: Estrogen-induced cholestasis results in a down-regulation of all basolateral organic anion transporters. The moderate decline in expression of Oatp1, -2 and -4 may explain the unchanged sodium-independent transport of bile acids due to overlapping substrate specificity. Reduction in transporter gene expression seems to be mediated by a diminished nuclear binding activity of transactivators such as HNF1, C/EBP and PXR by estrogens.

Animals↗
PubMed2003

Pharmacokinetics of high doses of intramuscular and oral heroin in narcotic addicts.

BACKGROUND: In several countries medical prescription of diacetylmorphine is currently being evaluated as a treatment option for heavily dependent narcotic addicts. Because of damaged veins, many patients administer diacetylmorphine intramuscularly or orally. Therefore we characterized the pharmacokinetics of intramuscular and oral diacetylmorphine in the high dose range usually required in narcotic addicts. METHODS: Three intramuscular doses, 3 oral doses, and 1 intravenous dose of diacetylmorphine and oral and intravenous test doses of deuterium-labeled morphine (morphine-N-methyl-d3 [morphine-d3]) were administered to 8 heroin-addicted patients. Arterial plasma concentrations of diacetylmorphine, monoacetylmorphine, morphine, morphine-3-glucuronide, morphine-6-glucuronide, and morphine-d3 were measured by liquid chromatography-mass spectrometry. RESULTS: Intramuscularly administered diacetylmorphine (</=200-250 mg) exhibited linear diacetylmorphine, monoacetylmorphine, and morphine kinetics and resulted in sustained diacetylmorphine exposures (bioavailability, 380% +/- 157% [mean +/- SD]) and in lower and delayed peak monoacetylmorphine and morphine concentrations as compared with intravenous administration. Oral diacetylmorphine (</=600 mg) yielded negligible systemic diacetylmorphine and monoacetylmorphine exposures but was associated with linear kinetics and high bioavailabilities for morphine (67% +/- 19%), morphine-3-glucuronide (205% +/- 52%), and morphine-6-glucuronide (180% +/- 61%). In addition, oral diacetylmorphine was absorbed more rapidly and to a greater extent than a concomitant test dose of morphine-d3. CONCLUSIONS: On the basis of the linear pharmacokinetics, the high bioavailability of intramuscular diacetylmorphine, and the rapid and extended morphine absorption from oral diacetylmorphine, the intramuscular and oral routes can be recommended as safe and feasible alternatives to the intravenous route for medical prescription of diacetylmorphine.

Administration, Oral↗